updated March 2019
Nazareth D'Silva's family is relevant because there is a DNA match between a descendant of Felix, one of Nazareth's sons, and a descendant of William, one of Francis D'Silva's sons.
It is possible that Nazareth and Francis were brothers or cousins. A common occupation of several members of the two families was involved with education.
Sources of the information I have are: British Library and familysearch.com births, marriages and burial records and Thackers directories.